M. F. Plateau on the Centre of Gravity in Insects. 55 



The specimen only differs from Mr. Hallowell's figure in 

 being marked with brown lines beneath, and in having more 

 elongate claws ; and I strongly suspect that they are both the 

 same species. 



VII. — Experimental Researches upon the Position of the Centre 

 of Gravity in Insects. By Felix Plateau*. 



The study of the conditions of equilibrium of living crea- 

 tures, I need scarcely say, is only possible when we know in 

 each of them the situation of the centre of gravity. Now that 

 the knowledge of the mechanics of the Articulata has made 

 considerable progress, thanks to the employment of processes 

 of investigation borrowed from physics, it seemed to me that 

 it would be really useful to describe an easy method of inves- 

 tigating the centre of gravity of the Articulata, and to give an 

 account of the results which its application to insects has en- 

 abled me to obtain. 



Unfortunately I cannot, in a mere summary, give a descrip- 

 tion of the instrument I have employed. A mere short de- 

 scription without a figure is of necessity obscure and of no use 

 at all. I shall only say that this instrument nearly reproduces, 

 on a small scale and with some improvements, that which was 

 invented by Borelli to determine the position of the centre of 

 gravity in man. As to the results of my experiments, I must 

 likewise refrain from giving them under the form which they 

 take in my memoir — that is to say, in the shape of a consider- 

 able number of figures brought together in several tables. I 

 shall therefore confine myself to the indication of the general 

 conclusions which I have thought I might deduce from them, 

 supporting these, where necessary, by a few examples. 



1. The centre of gravity of insects is situated in the vertical 

 median plane which passes through the longitudinal axis of 

 the body. 



2. It occupies a very nearly identical position in insects of 

 the same species and of the same sex in the same attitude. 



3. It is rarely that the external form of the body allows us 

 to determine, without ex/periment^ the exact position of the 

 centre of gravity. I shall cite, as an example, the results 

 fin-nished by the family of the Odonata. All its representa- 

 tives have nearly the same external aspect ; and yet, notwith- 

 standing this quasi-identity of structure, I have foimd the 



* Biblicftlieque Universelle : Archives des Sciences Physiques et Na- 

 turelles, tome xliii. 1872, from an abstract communicated by the author. 



